

A220816


Number of rooted binary MULtrees with n leaves on the label set [3].


2



3, 6, 18, 75, 333, 1620, 8208, 43188, 232947, 1282824, 7178598, 40711158, 233445483, 1351255608, 7884677052, 46330220604, 273905815095, 1628113352418, 9724235975136, 58330497033576, 351252593186211, 2122598374680816, 12867757823745036, 78235685862460893
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OFFSET

1,1


LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..200
V. P. Johnson, Enumeration Results on Leaf Labeled Trees, Ph. D. Dissertation, Univ. Southern Calif., 2012.


MAPLE

a:= proc(n) option remember; `if`(n<2, 3*n, `if`(n::odd, 0,
(t> t*(1t)/2)(a(n/2)))+add(a(i)*a(ni), i=1..n/2))
end:
seq(a(n), n=1..25); # Alois P. Heinz, Sep 23 2018


MATHEMATICA

a[n_] := a[n] = If[n < 2, 3 n, If[OddQ[n], 0, (# (1  #)/2 &)[a[n/2]]] + Sum[a[i] a[n  i], {i, 1, n/2}]];
Array[a, 25] (* JeanFrançois Alcover, Sep 02 2019, after Alois P. Heinz *)


CROSSREFS

Column 3 of A319539.
Sequence in context: A178789 A102962 A076510 * A038060 A135504 A307334
Adjacent sequences: A220813 A220814 A220815 * A220817 A220818 A220819


KEYWORD

nonn


AUTHOR

N. J. A. Sloane, Dec 22 2012


EXTENSIONS

a(7) corrected and terms a(11) and beyond from Andrew Howroyd, Sep 22 2018


STATUS

approved



